Efficiency analysis of a three-phase power transformer

By R Gouws and O Dobzhanskyi, North-West University


Published in:

Electricity+Control, August 2015 (pages 36 – 41)

Enquiries: Rupert Gouws. Email Rupert.Gouws@nwu.ac.za


Read the full article on Efficiency analysis of a three-phase power transformer in PDF format.


The efficiency of a three-phase power transformer is affected by power losses. There are two main sources of losses: Winding and core losses which contribute to the total losses of the electrical system [5]. Core losses consist of the hysteresis losses in the magnetic core of the transformer. Winding losses consist of the losses in the primary and secondary windings. They depend on the load current and are found as [5]. There are associated losses owing to harmonics but they can be neglected assuming that the supply voltage of the transformer is not distorted [6, 7, 8]. That is why it is crucial to operate a transformer as close as possible to its rated load condition.

The materials which are required to conduct the practical tests at any industry and in a heavy current laboratory are:

• Three-phase transformer
• Three-phase voltage supplier
• Ammeter or multi-meter
• Current transformer
• Voltmeter
• Two wattmeters
• Connection wires


Take note

  • Many plants are served by a supply system that includes on-site transformers and substations.
  • Transformer efficiency is an increasingly important parameter to understand, and the efficiency improves wont loading (within the specified operating range).
  • Open and short circuit tests can be effectively used to determine the machine parameter, and hence determine its efficiency.


* Read full article (pdf) for references.